Add implicit dart:core import when resynthsize from Kernel.

pkg/analyzer/test/src/summary/resynthesize_kernel_test.dart

 // Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library analyzer.test.src.summary.resynthesize_kernel_test;
 
 import 'dart:async';
 
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/file_system/memory_file_system.dart';
 import 'package:analyzer/src/dart/element/element.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/kernel/resynthesize.dart';
 import 'package:analyzer/src/summary/resynthesize.dart';
 import 'package:front_end/compiler_options.dart';
 import 'package:front_end/file_system.dart';
+import 'package:front_end/src/base/libraries_specification.dart';
 import 'package:front_end/src/base/performace_logger.dart';
-import 'package:front_end/src/base/libraries_specification.dart';
 import 'package:front_end/src/base/processed_options.dart';
+import 'package:front_end/src/byte_store/byte_store.dart';
 import 'package:front_end/src/fasta/uri_translator_impl.dart';
-import 'package:front_end/src/byte_store/byte_store.dart';
 import 'package:front_end/src/incremental/kernel_driver.dart';
 import 'package:kernel/kernel.dart' as kernel;
 import 'package:kernel/target/targets.dart';
 import 'package:kernel/text/ast_to_text.dart' as kernel;
 import 'package:kernel/type_environment.dart' as kernel;
 import 'package:package_config/packages.dart';
 import 'package:path/path.dart' as pathos;
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 import '../context/mock_sdk.dart';
@@ skipping 462 matching lines @@
   test_import_deferred() async {
     await super.test_import_deferred();
   }
 
   @failingTest
   test_import_invalidUri_metadata() async {
     await super.test_import_invalidUri_metadata();
   }
 
   @failingTest
-  test_import_self() async {
-    await super.test_import_self();
-  }
-
-  @failingTest
   test_inferred_type_refers_to_function_typed_param_of_typedef() async {
     await super.test_inferred_type_refers_to_function_typed_param_of_typedef();
   }
 
   @failingTest
   test_inferred_type_refers_to_function_typed_parameter_type_generic_class() async {
     await super
         .test_inferred_type_refers_to_function_typed_parameter_type_generic_class();
   }
 
@@ skipping 432 matching lines @@
   @override
   Future<List<int>> readAsBytes() async {
     return file.readAsBytesSync();
   }
 
   @override
   Future<String> readAsString() async {
     return file.readAsStringSync();
   }
 }